1. Field of the Invention
The current invention relates to a feedback controller having multiple feedback paths. Particularly, although or exclusively, the current invention also relates to a feedback controller having multiple feedback paths which can be used as a pulse width modulation control circuit for a switch mode power supply.
2. Background Information
Pulse width modulation control circuits are well known and are widely used in switch mode power supplies. A typical controller has a feedback path that compares a sample of the power supply output with a referenced voltage and generates an error signal for a PWM control circuit that varies the duty cycle of the power supply switching device in response to the value of the error signal. As with all control systems there is a trade-off of between stability and response time. Controllers having low bandwidth always provide very stable control characteristics, but react slowly to large changes in the output voltage of the power supply. Controllers having a high bandwidth react quickly to large changes in the output but can be difficult to stabilize especially in noisy environments or in power supply supplying quickly changing loads. Various control strategies and circuits are available which purport to solve these problems including voltage-mode control, current-mode control, one-cycle control, feed forward, feedback and V Square control systems. While all of these different methods having their own advantages and disadvantages which might suit particular applications there still remains a trade-off between stability and speed of response of the control circuit.
It is an object of the present invention to provide a feedback controller having multiple feedback paths that provides improved response to step load changes in voltage output of a power supply while still providing stable regulation under constant or slowly varying load conditions. It is a further object of the present invention to provide a feedback controller having multiple feedback paths which ameliorates at least some of the problems associated with known feedback controllers or which at least provides the public with a useful alternative.